Stoichiometry of Signalling Complexes in Immune Cells: Regulation by the Numbers

1. Introduction
Host protection against pathogens and tumor cells is mediated mainly via white blood cells
or leukocytes. As an inappropriate immune response can result in damage to the host
and/or failure in pathogen clearance, the activation and function of leukocytes are tightly
regulated processes. Regulation of immune cells is carried out by complex networks of
receptors and cellular mediators. While the progress of the signal cascade is necessary for
leukocyte activation and the development of an immune response, improper signaling and
cellular activation are associated with various pathologies. The study of such networks
constitutes a cornerstone of immunological research and has great implications for the
understanding of the immune system and for the development of immunotherapies for
cancer, infectious diseases, as well as autoimmunity.
In this chapter, we will describe the importance of the stoichiometry of signalling complexes
in the regulation of leukocyte activation and function. We will focus on techniques used to
analyze the formation, composition, and stoichiometry of multiprotein complexes, and we
will also review current information and implications of stoichiometry on immune-cell
activation and regulation.